The insudative theory is one of the four main theories of antherogenesis and can explain many of the risk factors associated with atherosclerosis. Injury to the endothelial cell occurs and the permeability of the endothelial cell is altered. Cholesterol and other lipid components of very low density lipoproteins and low density lipoproteins enter the arterial wall and interact with connective tissue components and the process of atherosclerosis begins. Vitamin D is one of the many biological compounds that injures the endothelial cell and induces atherosclerosis. Early changes in vascular permeability will be determined by the uptake of and binding of calcium to the arterial wall and cellular components thereof. Specific areas of the arteries with altered permeability can be detected by uptake of dyes. An alteration in the permeability of cellular membranes to calcium will result in a change in the intracellular concentration of calcium. Since calcium affects numerous biochemical processes, the metabolism of the cellular components may change. Compounds that inhibit the formation of the atheroscerotic plaque induced by vitamin D will be adminsitered to rats in order to determine whether or not these compounds prevent the change in cell permeability to calcium perhaps reflecting a protective effect for the endothelial cells. An alteration in the permeability of calcium may occur before one detects the change in permeability to the large lipoprotein molecules. The regression of plaques by specific compounds will be followed with time after replacing the atherogenic diets with the basal diet. The blood appears to have a protein that stimulates the uptake of calcium into bone cells. This protein may be a vitamin D dependent protein. Since vitamin D injures endothelial cells, induces atherosclerosis and increases the deposition of calcium and lipids in the arterial wall, the protein will be assayed in serum from atherosclerotic rats. Does vitamin D increase the serum protein concentration and thus increase the uptake of calcium by the arterial wall and cellular components thereof?